1. Field of the Invention
The present invention relates generally to the fields of cell biology, biochemistry and medicine. More particularly, it concerns use of soluble factors produced by probiotic bacteria for the inhibition of epithelial cell apoptosis, including gastrointestinal disorders.
2. Description of Related Art
Inflammatory bowel diseases (IBD) are characterized by increased production of inflammatory cytokines, epithelial cell apoptosis, and immune cell infiltration, leading to disruption of the intestinal epithelial integrity (Sartor, 2002). Therefore, remission of these disorders requires both decreased apoptosis and restitution of the damaged epithelium. Recent studies reveal several potential therapeutic approaches to induce restitution of the damaged epithelium. Growth factors (El-Assal and Besner, 2005; Matsuura et al., 2005; McCole et al., 2005; Sinha et al., 2003) and cytokines (Marini et al., 2003; Zeissig et al., 2004) have been reported to modulate these processes by regulating proliferation (Matsuura et al., 2005), migration (El-Assal and Besner, 2005), and apoptosis (Marini et al., 2003; Zeissig et al., 2004).
Increasing evidence suggests some commensal bacteria enhance intestinal epithelial homeostasis and barrier integrity. Indeed, commensal bacteria regulate a number of host processes, including nutrition, development, and immune responses, that are relevant for both health and disease (Yan and Pol, 2004). Therefore, manipulation of intestinal bacterial flora has been used as an alternative health approach for disease prevention and treatment (Sartor, 2004). Living microorganisms in the intestinal tract which benefit the host are termed probiotics (Lilly and Stillwell, 1965). Recent studies indicate that some Lactobacillus species function as probiotics and induce sustained remission in ulcerative colitis and pouchitis (Borody et al., 2003; Dieleman et al., 2003; Mimura et al., 2004; Schultz et al., 2004). Lactobacillus rhamnosus GG (LGG), a bacterium used in the production of yogurt, is one of the best-studied Lactobacillus strains in clinical trials for IBD.
The presumed first target of probiotic actions is the intestinal epithelial cell. Probiotic bacteria stimulate several intestinal epithelial cell protective responses, including enhancement of epithelial barrier function (Resta-Lenert and Barrett, 2003; Resta-Lenert and Barrett, 2006), mucin synthesis and secretion (Mack et al., 2003; Otte and Podolsky, 2004), inhibition of enteropathogenic E. coli binding (Mack et al., 2003), and cell survival (Yan and Polk, 2002). However, the mechanisms regulating epithelial responses to probiotics are complex and mostly unknown. The inventors have used LGG to investigate molecular mechanisms by which probiotics regulate intestinal epithelial cells, and previously reported that LGG prevents cytokine-induced apoptosis in both human and mouse intestinal epithelial cells through activating Akt and inhibiting p38 mitogen activated protein kinase (MAPK) activation (Yan and Polk, 2002). Akt plays a central role in promoting cell survival by inactivation of several proapoptotic pathways, including BAD, caspase 9 and caspase 3, and stimulating cell proliferation by activation of cell cycle regulators, such as cyclin/CDK (Amaravadi and Thompson, 2005; Hanada et al., 2004). They have further reported that soluble factors recovered from LGG culture broth supernatant (LGG-s) activate Akt in a phosphatidylinositol-3′-kinase (PI3K)-dependent manner and prevent cytokine-mediated apoptosis (Yan and Polk, 2002). One recent report has shown that soluble factors present in LGG conditioned-medium (LGG-CM) induce cytoprotective heat shock protein synthesis in intestinal epithelial cells (Tao et al., 2006). However, to the inventors' knowledge, the specific components of LGG-s that promote intestinal epithelial health have not been identified. Therefore, purification and characterization of LGG-derived soluble proteins that regulate intestinal epithelial cell proliferation and survival is needed.